Ganglioside G_M3 overexpression induces apoptosis and reduces malignant potential in murine bladder cancer

We demonstrated previously (S. Kawamura et al., Int. J. Cancer, 94: 343-347, 2001) that large amounts of ganglioside GM3 accumulate in superficial bladder tumor, compared with invasive bladder tumors and that exogenous G_M3 inhibits the invasive potential of bladder tumor cells. To apply the G_M3 overexpression system to bladder tumor therapy, direct evidence for the important role of G_M3 in bladder tumor invasion must be obtained through transfer of the gene responsible for G_M3 overexpression. To determine the most appropriate cancer cell line for elucidating the antitumor effect of ganglioside G_M3 overexpression, the present study examined glycolipid composition, enzyme activity, and mRNA expression of the glycosyltransferases responsible for G_M3 synthesis in the bladder tumor cell lines KK-47, J82, MGH-UI, YTS-1, and MBT-2. A murine bladder carcinoma cell line (MBT-2) was transfected with a GM3 synthase [(lactosylceramide α2,3-N-acetyl sialic acid transferase); sialyltransferase-I; SAT-I] cDNA, because this line does not naturally express G_M3. Stable transfectants (MBT-2-SAT-I) that overexpressed G_M3 were characterized by a reduced potential for cell proliferation, motility, invasion, and xenograft tumor growth, and an increase in the number of apoptotic cells. In the proportion of synthetic S phase, cells did not differ between MBT-2-SAT-I and mock-transfectant cells. These results suggest that the decreased proliferative potential related to G_M3 overexpression was attributable to the increased number of apoptotic cells. Although details of the mechanism of apoptosis remain unclear, the overexpression of G_M3 by gene transfer of SAT-I may present a novel therapeutic modality.